Method for coating paper with pressure rupturable fluid containing capsules

ABSTRACT

The invention in a machine and method for &#39;&#39;&#39;&#39;on-the-machine&#39;&#39;&#39;&#39; coating of a paper web to coat one surface of the paper web with a uniform distribution of pressure rupturable liquid containing capsules wherein the papermaking machine is provided with a printing couple while the paper is in a substantially uncured state with one roll of the couple comprising an impression roller having a resilient surface and the other roll comprising a printing roll having a multiplicity of cells uniformly distributed in closely spaced-apart relation in the peripheral surface of the roll with means for application of the fluid composition containing the rupturable capsules in suspension onto the peripheral surface of the roll in an amount at least sufficient to fill the cells and means for doctoring the peripheral surface of the roll to remove coating composition from the area between the cells whereby, when the paper web is advanced in pressure contact between the roll pair, substantially pressureless transfer occurs of the coating composition in the cells to the adjacent side of the paper web to coat the paper web with the pressure rupturable capsules as a continuous operation with papermaking.

United States Patent [72] Inventor Thomas W. Busch Appleton, Wis.

[21] Appl. No. 705,076

[22] Filed Feb. 13, 1968 [45] Patented Dec. 28, 1971 [73] AssigneeAppleton Coated Paper Company Appleton, Wis.

[54} METHOD FOR COATING PAPER WITH PRESSURE RUPTURABLE FLUID CONTAININGCAPSULES 8 Claims, 6 Drawing Figs. [52] US. Cl 162/184, 117/156,118/212, 162/158, 162/162, 162/174 [51] Int. Cl D21d 3/00 [50] Field ofSearch 162/1 19,

3,384,536 5/1968 Sandberg et a1.

Primary Examiner-S. Leon Bashore Assistant Examiner-Frederick FreiAttorney-McDougall, Hersh, Scott and Ladd ABSTRACT: The invention in amachine and method for onthe-machine coating of a paper web to coat onesurface of the paper web with a uniform distribution of pressurerupturable liquid containing capsules wherein the papermaking machine isprovided with a printing couple while the paper is in a substantiallyuncured state with one roll of the couple comprising an impressionroller having a resilient surface and the other roll comprising aprinting roll having a multiplicity of cells uniformly distributed inclosely spaced-apart relation in the peripheral surface of the roll withmeans for application of the fluid composition containing the rupturablecapsules in suspension onto the peripheral surface of the roll in anamount at least sufficient to fill the cells and means for doctoring theperipheral surface of the roll to remove coating composition from thearea between the cells whereby, when the paper web is advanced inpressure contact between the roll pair, substantially pressurelesstransfer occurs of the coating composition in the cells to the adjacentside of the paper web to coat the paper web with the pressure rupturablecapsules as a continuous operation with papermaking.

METHOD FOR COATING PAPER wmi PRESSURE RUI'IURABLE FLUID CONTAININGCAPSULES This invention relates to paper base material havingrupturable, liquid containing, microcapsules on one surface thereof andto a new and improved method for the preparation of same.

Paper of the type described finds many uses, as will hereinafter bedescribed. Most representative for the present is usage as one of thecomponents of a carbonless copy paper system in which use is made of onesheet having the layer of microcapsules containing undeveloped oilsoluble dyes dissolved in droplets of a water insoluble organic fluid.The droplets are encased in a thin wall of tanned gelatin in the form ofmicrocapsule aggregates having an average diameter within the range of 8to 12 microns. The other component employed in combination with thedescribed capsule containing sheet is a sheet of paper having a specialmineral or clay coating adapted to be positioned in intimate contactwith the capsular coating in the assembly for transfer of underdevelopeddye liquid from the ruptured capsules to the adjacent mineral coatingfor development of the dye color.

In a conventional commercial assembly, the carbonless copy paper systemconsists of a first or top sheet coated on its back side with themicrocapsules and a second sheet coated on its front side with thespecial mineral coating. In a typical multiple sheet assembly, such as afive-part sales form, the three intermediate sheets will be coated ontheir front sides with the special mineral coating and on their backsides with the described microcapsular system while the top sheet iscoated on its .back side only with the microcapsular system and thebottom sheet coated only on its top side with the special mineralcoating.

The front or special mineral coating more closely resembles an ordinarypaper coating. Since it does not contain any rupturable or otherpressure sensitive materials, it can be produced economically andsuccessfully as a coating applied as a part of the continuouspaperrnaking process since it can be calendered or finished, as the casemay be.

Because the microcapsules are pressure sensitive and are capable ofbeing ruptured in response to pressure of the magnitude encountered inmechanical nips of a paper machine, it has been the practice to makeapplication of the microcapsular system as a separate operation appliedonto the previously fabricated paper base sheet. For this purpose, usehas been made of a composition in which the microcapsules are admixedwith adhesive, lubricating pigment such as talc, and cellulosic fiberswhich operate to protect the capsules from premature rupture in thecoating.

The described ofi'-the-machine coating of the microcapsular system posesa number of requirements including I additional machinery for suchseparate off-the-machine coating; (2) additional floor space for suchseparate operation and equipment; (3) movement of paper from thepaperrnaking machine to the described separate coating operation inwhich packaging, shipping and labor represent additional costs; (4)additional waste resulting from a two-stage process, and (5) procurementof paper as a separate commodity with its attendant costs, etc.

Thus it is an object of this invention to provide a new and improvedmethod and means for the production of a paper base material havingrupturable microcapsular material on at least one surface thereof and itis a related object to provide a method of the type described which canbe carried out on the paperrnaking machine materially to reduce the costthereof; which provides for economical and efficient utilization of theencapsulated material; which provides for uniform coating of theencapsulated material in a layer well bonded or integrated with thepaper base sheet; and which can be applied as a continuous operationwithout an excessive rupture of the capsules and which produces aproduct of good appearance and capable of use in the development of copyof good quality.

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, an embodiment of the invention is shown in the accompanyingdrawings in which FIG. I is a detailed elevational view of the rollapplicator embodying the features of this invention;

FIG. 2 is a partial plan view of the roll surface formed with pyramidcells;

FIG. 3 is a view similar to that of FIG. 2 with the surface formed withtrihelical cells;

FIG. 4 is a view similar to that of FIGS. 2 and 3 with the surfaceformed with quadrangular cells;

FIG. 5 is a view similar to that of FIG. 2 with the surface formed ofhexagonal cells; and

FIG. 6 is a schematic view of a paperrnaking machine embodying thefeatures of this invention.

In accordance with the practice of this invention, application of themicrocapsules is made at a point in the operation of the paperrnakingmachine which occurs after the web has been formed as an uncured web orpartially cured web so that the applied coating will enable the capsulesto become partially embedded with the fibrous structure on the surfaceof the paper while, at the same time, eliminating the uneconomicalfeatures of excessive capsule loading of the paper web or loss ofcapsules with the water drained from the sheet during the web formingprocess.

In the preferred practice of this invention, modification is made of apaperrnaking machine at a point after the web has been formed but beforethe internal water resistance of the paper web has been developed, toinsert a processing step for application of the microcapsule containingcoating composition. For this purpose, use is made of a roll pairbetween which the formed web 10 is passed for engagement between theperipheral surface of the rolls. One roll 12 of the roll pair is formedpreferably, but not necessarily, with a surface 14 of resilient materialwhile the other roll 16 of the roll pair is in the form of a cylindricalroll having its peripheral surface etched or otherwise formed to definea multiplicity of closely spaced cells and which has a doctor blade orwiper 18 in engagement with the peripheral surface of the etched roll 16in advance of engagement with the web 10 to remove coating compositionfrom the surface other than that filling the cells thereby to provide adirect gravure type printing station for the pressureless application ofthe capsular coating in uniform distribution onto the surface of thepaper web 10 as the peripheral surface of the cylinder 16' comes intocontact with the one side of the paper web.

The applicator cylinder 16 is etched, engraved or otherwise formed withthousands of minute recessed cells which are capable of being filledwith the emulsion of rupturable microcapsules with the lands between thecells forming the relatively true cylindrical surface. The cells can beformed with various configurations such as of the type referred to inthe rotogravure art as pyramid cells, trihelical cells, quadrangularcells, hexagonal cells and the like cells of various cross sections orconfigurations uniformly distributed over the entire peripheral surfaceof the cylinder. The depth of the cells will be efiective to determinethe amount of fluid retained in the cells after the peripheral surfaceof the cylinder has been cleaned by the wiper blade 18.

As the etched cylinder revolves, the lower portion, immersed in a bath20 of capsular coating composition, picks up an excess of liquid on itssurface. Surplus liquid is removed by the doctor or wiping blade 18 toleave the surface clean while capsule containing liquid remainssubstantially to fill the cells. A system of the type described isself-flushing whereby any foreign fibers or material picked off the webwill be removed so that little will remain on the roll surface tointroduce defects in the applied coating.

As the cylinder continues to revolve, the capsule containing fluidcomposition remaining in the cells transfers from the cylinder to theadjacent surface of the web in response to pressure exerted by theresilient surface 14 of the impression roll 12 of the roll pair. Theimpression roll presents the web 10 against the surface of the etched orengraved roll 16 whereby the capsule containing liquid becomes displacedfrom the cells to the web primarily by capillary action and the affinityof the uncured paper for the capsule containing fluid.

Because the resilient surface of the impression roller 12 makes uniformcontact across the face of the engraved or etched cylinder 16 andbecause pressure is hydraulically applied, variation in paper thicknesshas little influence on the uniform distribution of the capsulecontaining liquid thereby to provide for uniformity in deposition fromrun to run and over large runs. By proper selection of cell dimension,such as width, depth and shape, it becomes possible to effect uniformcontrol of coating weight.

Since the capsules are applied during a stage of web formation whichenables the capsules partially to become embedded in the fibers at thesurface of the web, it becomes possible to make use of a coatingcomposition of emulsified capsules without the need of floc and/orcellulosic fibers for protection of the capsules, as in compositionsheretofore employed in offthe-machine coating although such materialsmay be employed in coating compositions applied in accordance with thepractice of this invention if necessary.

It will also be apparent that the capsule containing liquid retained inthe cells is not subjected to excessive pressures for transfer such thatthe capsular coating can be transferred in any desired concentrationwithout the danger of capsule rupture, as in other coating processes.

It will be apparent further that the overall pattern of cells in thesurface of the applicator cylinder will provide for the printing of arelatively uniform and substantially continuous coating over the entiresurface of the paper web with application thereof being made to thesurface so that the capsules will be deposited at the point for mostefficient utilization thereby to make maximum use of the capsules makingup the coating composition.

Since the composition of the capsule containing coating does notconstitute a part of this invention, detailed description thereof willnot be made. Suffice it to say that such coating composition may beformulated in an aqueous system containing capsules having an averagesize of from 7 to 9 microns, with or without starch, talc or floc, andin a solids concentration within the range of 18-24 percent in which theamount of emulsified capsules may be within the range of l3-22 percent.The composition can be applied in appropriate coating weights of 2% to3% pounds per 3,300 square feet of surface area.

By way of example, use can be made of a cylinder having a 50 trihelicaletch pattern corresponding to 30-40 micron bridges and 48-50Xl0 cubicmicron cell volume.

Having described the basic concepts of this invention, illustration willnow be made with respect to the utilization thereof as a part of aconventional papermaking machine.

Referring now to FIG. 6 of the drawing, illustration is madeschematically of a typical papermaking machine which operatescontinuously to produce an endless web of paper but which has beenmodified to embody the printing couple of this invention. The machineincludes a head box 30 at the head end of the machine which contains thepulp slurry that is spread uniformly over the width of the continuouslymoving endless screen 32 which filters the cellulose fibers ininterfelted relationship on the surface thereof to produce the wet web34 as water drains through the screen 32. By the time the web reachesthe delivery end of the screen, it has adequate self-sufficiency topermit removal from the screen for passage first through a series offelted press rolls to compact the web of interfelted fibers and thenthrough a drying section 38 which reduces the amount of water in thepaper web. Before the paper web is completely dried and before it iscalendered and preferably while it is still in the uncured stage, thepaper web is advanced in continuous fashion and at forming speed throughthe printing couple including the impression roller 12 and the engravedprinting roller 16 whereby the coating of emulsified capsular materialis transferred by substantially pressureless transfer onto the ad'acentside of the paper web. Thereafter the coated paper we can be furtherprocessed as by advancement through driers 40 and finishing rolls 42,with and preferably without light calendering before the coated paperweb is collected on the reel 44 and subsequently sheeted. As in the casewith conventional on-the-paper-machine coating, supplementary drying orTeflon covered drier drums may be required following the coatingapplication to prevent transfer of the wet coating to the drier drumsurface. This may be required to make the process practical at highspeeds, but it is not foreign to the papermaking art.

The impression roll 12 may be formed of a rubber roll having a metalliccore or it can be formed of a metal roll having a surface coating orblanket of resilient, rubberlike material. The rolls are adapted to bedriven by conventional means at a peripheral speed corresponding to thelinear speed of the paper in the paper-forming operation.

Aside from the described use as a colorless carbon system, the sheetwith the capsular coating finds many other uses, such for example as awiping cloth when the capsules are filled with a suitable lubricantliquid or dusting liquid, as a pressure sensitive label or wall paperwhen the capsules are filled with a liquid adhesive, as a cologne whenthe capsules are filled with suitable perfume oils, and numerous otherapplications which will become obvious.

It will be understood that changes may be made in the details ofconstruction, arrangement and operation without departing from thespirit of the invention, especially as defined in the following claims.

I claim:

1. An on-the-machine" coating method for producing a sheet of paperhaving a surface coated with pressure rupturable fluid containingcapsules comprising the steps of passing a paper web continuously beforeit has been completely cured through a roll couple, one of which is animpression roll and the other of which is a printing roll having anoverall pattern of uniform closely spaced cells in the peripheralsurface, wetting the peripheral surface of the latter roll with a fluidcomposition containing the rupturable capsules in unifonn suspensiontherein and in amounts to at least fill the cells, removing excesscoating composition from the peripheral portion of the roll between thecells before the peripheral surface of the roll comes into contact withthe paper web and then bringing the peripheral surface of the printingroll into contact with one side of the paper web while the opposite sideis engaged by the impression roll whereby fluid coating compositiontransfers without excessive pressure from the cells to the adjacentsurface of the paper web to coat the surface of the paper web with thepressure rupturable capsules.

2. The method as claimed in claim I in which the roll couple makespressure engagement with the opposite surfaces of the paper web as it isadvanced therebetween.

3. The method as claimed in claim 1 in which the paper web is in theform of an uncured paper at the time that it is advanced between theroll couple.

4. The method as claimed in claim 1 in which the impression rollcomprises a roll formed of a resilient material.

5. The method as claimed in claim 1 in which the impression roll is ametal roll having a blanket formed of a resilient material.

6. The method as claimed in claim 1 in which the cells in the printingroll are etched into the surface of the roll.

7. The method as claimed in claim I in which the cells in the printingroll are engraved in the surface of the roll.

8. The method as claimed in claim 1 which includes the step of dryingthe applied coating.

2. The method as claimed in claim 1 in which the roll couple makespressure engagement with the opposite surfaces of the paper web as it isadvanced therebetween.
 3. The method as claimed in claim 1 in which thepaper web is in the form of an uncured paper at the time that it isadvanced between the roll couple.
 4. The method as claimed in claim 1 inwhich the impression roll comprises a roll formed of a resilientmaterial.
 5. The method as claimed in claim 1 in which the impressionroll is a metal roll having a blanket formed of a resilient material. 6.The method as claimed in claim 1 in which the cells in the printing rollare etched into the surface of the roll.
 7. The method as claimed inclaim 1 in which the cells in the printing roll are engraved in thesurface of the roll.
 8. The method as claimed in claim 1 which includesthe step of drying the applied coating.